Integrated circuits are multi-layer structures produced by applying a sequence of layer-deposition and patterning processes to a semiconductor wafer. Various steps in the manufacture of semiconductor devices require measurements of thickness or other characteristics (e.g., optical parameters) of each layer in the multi-layer wafer structure.
Optical methods for on-line or integrated measurement of the parameters of dielectric films (e.g., film thickness) are known in the art. Most of these techniques are based on reflectometry in a broadened spectral range, e.g. ranging from DUV to NIR spectral range.
In order to determine the parameters of the uppermost layer in the wafer stack (e.g., thickness of this layer), it is especially important to determine optical properties of each layer (film) of the actual stack after completing all the processing steps. Unfortunately, in cases when measurements are performed on the entire stack including different layers that similarly affect the spectral response of the stack, accurate determination of the properties of each separate layer are almost impossible.